Sound translating device



Oct. 16, 1934.

, H. R. VOORHEES SOUND TRANSLATING DEVICE Filed De. 18. 1951 R O m w A I Q 'fiaroldfilvoorhees,

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Patented Oct. 16, 1934 SOUND TRANSLATING DEVICE Harold R. Voorhees, Merchantville,-N.- J., assignor to RadioCorporation of America, a. corporation of Delaware Application December 18, 1931,Serial No. 581,792 9Claims. (01. 174-1155) My invention relates to sound translating de: vices and, more particularly, to loudspeakers of the electro-dynamic type.

In the operation of electro-dynamic loud- V speakersof the high-power type, it is necessary to transmit large mechanical forces from the voice coil to a heavy, substantially inflexible cone structure at frequencies which adequately cover the usual voice or music range. To do this satisfactorily, necessitates a voice coil andsupporting structure of great rigidity, but of minimum mass.- It is also imperative that the voice coil itself shall have a relatively large diameter and that it shall be so rigidly supported as to maintain its circular shape, especially in the event that soft, highly conductive wire is used for the coil. 7

Should the loudspeaker be destined for use in situations exposed to the weather, such as in church belfries and the like, it is a furtherrequirement that the cone and the voice coil be substantially unaffected by heat and moisture.

In view of the fact that the field current required by high-power electro-dynamic speakers is quite large, it is obvious that an excessive amount of heat will be developed during their operation, which heat would ordinarily have a deleterious effect upon the voice coil and also upon the insulation used on the wire constituting the field winding. Heretofore, the heat developed has been a serious limitation upon the power that aloudspeaker of the described type could handle, I I

, Furthermore, .when voice coils of large diameter are used to actuate proportionately-large conical diaphragms, a large portion of the apex of the cone must necessarily be cut away suf ficiently to accommodate the coil form mounting. This cutting away destroysan area of the cone which, otherwise, would be elfective in radiating high frequencies by reason of j its low massfactor and its contiguity to the locus of application of the driving force. V It is, accordngly, an object of my invention to provide a loudspeakerthat shall be capable of handling tremendous'power.

, A further object "of mylinvention is to provide an'improved voice coil that shall be rigid and not liable to be, deformed under large driving forces. A further object] of my invention is to provide, in a loudspeaker of the type described, heat radiating means that shallprevent excessive temperature, rise when the device is operatedj I I .A further object of my invention is to provide Referring tothe drawing, the essential features "of my loudspeaker include a multi-rsection field a composite diaphragm for loudspeakers of the high-power type that shall be equally as effective at high audio frequencies as at low audio frequencies. 60

Another object of my invention is to provide means, actuated by the voice coil when in motion, for causing a current of cooling air to pass over the said voice coil.

A still further object of my invention is to provide simplified and improved means of fastening external flexible leads to the moving coil structure of an electrodynamic speaker.

I The foregoing objects, and other objects appurtenant thereto, I prefer to accomplish by so formingthe voice coil by a molding process that the metallic conductor is imbedded in a mass of insulating material, preferablya phenol condensationproduot, such as bakelite, by providing the device with a plurality of heat radiating elements in intimate contact with the major metallic portions thereof,and by replacing the area of the diaphragm cutv away to accommodate the voice coil; mounting by a'small truncated cone, having an open end, coaxial with the main diaphragm.

v The novel features that I consider characteristicof my invention are set forthwith particularity in the appended claims. The invention itself, however, both as to its organization and its methodof operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawing, in which t Figure 1 is a view in perspective of my improved loudspeaker; I

Fig. 2 is a sectional view in elevation. of the device shown in Fig. 1, taken along a line corresponding to the line 2- -2 in the said figure;

Fig. 3 is asectional view, reduced in. size, ,in

elevation, taken along-a line corresponding to the 9 line 3-3 in Fig. 2; and

Fig. 4 is an enlarged sectional view' exemplify- .ing the manner inwhich my improved voice coil and mountingare constructed.

w'It is, of course, to be clearly understood that the actual device as commercially constructed is "many times larger than shown in the drawing,

Figsaland -2of thecdrawing being substantially onequarternatural size. x

coil 1 disposed axially on a center core 3 of a yoke 5 of magnetic material, a moving armature or coil structure '7 positioned in an annular air gap 9 of the magnetic field circuit of the yoke, and a 'large truncated cone diaphragm 11 secured at its small end to the moving coil in driven relation.

For the purpose of conducting away heat developed withinv the field structure of the speaker, I have provided a plurality of heat radiating elements such as plates orfins 13' of good heat conducting material; preferably copper,- having central openings 15 closely fitting around the center core 3, in thermal contact therewith, and extending outwardly for conducting away the heat. The field coil preferably is formed ina plurality of pancake sections as indicated,'"intercalated with the fins that are adapted to conduct away heat from many points within-thecoil structure.:

The outer portion of the yoke structure consists of a base plate 17 and an outer ring ,pole

piece 19 connected by spaced bars 21, forming" therebetween a plurality of openingsithrough which the heat conducting fins extend, preferably,

beyond the yoke; inheat radiating relation with the air. It is preferred, in some casesfthat the fins likewise makethermal contact with the bars l 21 of the yoke, for purposes of heat equalization (ranger'nent is more clearlyshown'in Fig.3. idesired, the conducting plates may be radially between the fins'and bars. The foregoing arslit to prevent a short circuit action uponthe' field coil with regard tounfiltered current pulsa- 1 tionstherein, particularly where'the field is used as a filter choke in the supply circuit.

The foregoing construction is very effective in reducing the he'atingof' the field structure. For

" the purposejof carrying away heat developed within'the voicei'coil structure! by'the voice currents, and to minimize" any conductionof 'heat from the pole .piece's iand l9 across/the air gap to the moving coil'structure, I haveprovided a small truncated'cone 25v secured at its base, as by cement, at or near the'small end of the large diaphragrn. 11 in reentrant relation therewith". The apex of the smallcone is provided with an open ing 2'7, through which'airisadapted to circulate.

I have found that this arrangement results in a pumping action for, effecting a unidirectional flow of a gaseous coolant such'as"air, 'asindicated by is drawn toward theinner pole-piece, thereby resulting in'a' pressure' area that is higher than that outside 'of the c.one,'-and causing a'flowof air from the high pressuretothe externallow pressuregarea. I When the cone movesin the opposite direction, there is developed substantially no difference in air pressures and hence'a uni-directional air flow results from' the foregoing dissimilar actionsi The air is caused to flow downwardly between the outer polepiece and the coil form by reason of the fact that the space under the airgap is closed, as: by a copper shading ring 28. -A felt compression ring 26 is; interposed between the ring 28 andithe top of the fieldi coil 1.

Otherwise, if the space were unconfined, there would bea flow of air'only upwardly between the inner pole piece and "th81 'C0l1f0Im, whereas flow 'on both sidesrof thecoil is desirable.; Inthe field structuresof sound producing devices of this type,

.having the outer-yoke inntheformof a closed shell of magnetic material, the space below the air gap is ordinarily closed to air leakage whereby an air now would be established down the outside of the moving coil, without the use of a seal such as the ring 28.

From the foregoing description, it will be seen that the pumping action of the small cone provides means responsive to the. signalling currents supplied to the voice coil for cooling .thelatter. It is also obvious that the flow of air serves to carry away some heat from the pole pieces. Likewise, the air may be caused to circulate over other portions of the magnetic field structure.

' In addition to the cooling effect caused by the small openended cone 25, the latter is effective in materially increasing the radiation of sounds or vibrations in the higher audio frequency range,

particularlybecause the small cone is in close driven relationwi'ththe moving coil, the high frequency vibrations generated in the coil 7 be ing imparted directly to the small cone independently of the vibrations imparted to the-large cone 1'1.' The size of the opening 27 in the apex of the small cone also controls the cushioning effect of the air confined between the inner core and the small cone and; hence controls appreciably the low frequency amplitude'of vibration of the large 0mm A Referring to-Fig.- 4, thevoice coil turns 6 and mounting form 7, according to 'myinvention, are

molded as a'single unit. The'formis composed of externaland internal sheets or-laminations 30 and 31,'respec tively, o'f fibrous material such as fabric or paper, or combinations thereofgimpregits nated' with a phenol-resin compoundg simiiar to bakelite of" such-a nature that, when cured or polymerized, gives "a rigid',*weather-'proof structure having a relatively small mass. This compound has the well known advantage that after polymerization it will not soften with heat. The turns of wire 6, preferably of enameled aluminum, are so embedded in themolded-formfl that there is no tendency for the turns to vibrate locally with respect to the form.

The-moving coil structure is constructed by impregnating the'fibrous layers, with the uncured phenol-resin, and; winding in proper sequence on a mandrel. The internal layers 31-are preferably of paper, and the external layers or covering 30 are preferably of a fabric such as silk. The voice coil winding is generously coated with the phenolresin compound-duringthe winding process. For

'the'purpose of forming a truncated conical flange 35 on one end of the coil form, for securing to the cone, thelaminated layers are preferabl'yradially slitat this end in such manner that, when wound fon the mandrel; the laminated' niaterial will be caused to assume the desired angleshown in the drawing;

V There may also be embodied in the above structure means for securingflexible terminalleads 37, for external circuit connectiona'to the ends 39 of the voice coil winding. In the present example n the: flange 35, although structure of thefiange 35, whereby after curing, the ends .ofjthesewi'res are heldrigidly and the flexible lead is brought out of the rim of the flange at a desired distance from the pole pieces. This constructionobviates the necessity of fastening let the flexible leads to'th'e diaphragm by various means, as has heretofore been the custom. When heat and pressure areapplied during the curing process, the phenol-resin 33 is forced completely around the wires, and the fabric and wires are formed into a compact, rigid, unitary structure that is so strong and light that large forces are adapted to be transmitted from the voice coil to the diaphragm at high audio frequencies without appreciable sound distortion and without danger of mechanical deformation of the parts of-the structure subjected to said forces.

In consonance Willhllhfi features of construction of the above rigid, weatherproof moving coil structure, the diaphragms 11 and are preferably. constructed of materials having similar durable properties. In the device that I have constructed and used, I have employed for the diaphragm layers of fabric and aphenol-resin compound, in a combination commercially known as micarta. It is preferable that the radial edges of the diaphragm, when the cone is formed, be brought together edge to edge and that an extra strip 41 be cemented and riveted thereto in order to secure the edges together. a This results in uniform diaphragm thickness at the small end of the cone for securing the same to the flange 35 of the coil form as shown, as by means of cement. If desired, a seamless cone may obviously be molded and, furthermore, it has been found desirable, in some cases, to mold the cone into a unitary structure with the coil form for purposes of maximum strength and great durability.

The moving coil is centered in the air gap by means of a resilient spider 43 secured at its center to the inner pole piece. The spider is preferably of light, flexible metal, such as phosphorbronze or duralumin, the arms of which have upturned ends 44 for attachment to the flange of the coil form as by rivets, and preferably securing the small end of the cone between the ends ie and the flange on the coil form. The base of the large cone is supported by the main framework 45 by means of an annular strip 47, preferably of rubberized fabric or other flexible material, that is secured at one edge to the framework and, at the other edge, to the base of the cone, in accordance with the usual practice.

By reason of the foregoing novel features of construction, I am enabled to provide a loudspeaker of the electro-dynamic type, having a greatly increased overall power rating for the production of tremendous volume of sound, which construction is particularly adapted to exposure in all kinds of weather and heat conditions. I have, furthermore, provided a loudspeaker having greatly improved acoustical properties under conditions of large volume of power.

Although I have disclosed but one embodiment of my invention, I am entitled to all changes in construction, within the spirit of the appended claims, that would occur to one skilled in the art. For example,although I have illustrated a loudspeaker having an electromagnetic field it is within the scope of my invention to employ a strong permanent, magnetic field in combination with the above described voice coil cooling means. It is further within the limits of my invention to use the above features of construction in connection with any sound translating device such as a transmitting microphone of the dynamic type for example.

I claim as my invention:

1. In a loudspeaker, a voice-coil and unitary sound-radiating and voice-coil cooling means associated therewith.

2. In an electrical translating device, means for simultaneously generating sound waves in accordance with undulat-ory signalling currents and for causing a flow of a coolant unidirectionally through said device.

3. In an electrical translating device, means adapted to move in response to undulatory signalling currents, and means associated therewith for simultaneously pumping a coolant unidirectionally through said device.

4. In a sound translating device, an armature of the moving conductor type adapted to carry heavy signalling current, means responsive to said current for causing a unidirectional fiow of air or other coolant over said armature,

5. In a sound translating device, a vibratory armature subject to undesirable heat conditions, a magnetic field structure having pole pieces adjacent said armature, and means operated by said armature for causing a cooling stream of air to flow between the poles and said armature.

6. In a sound translating device of the moving coil type, a magnetic field structure having an air gap in which'the moving coil is adapted to vibrate, means secured to said coil for causing a unidirectional flow of air up one side of said coil, and structure cooperating with said air gap and said means for causing a unidirectionalflow of air down the other side of said coil.

7. In a loudspeaker, a relatively large conical diaphragm adapted to radiate low frequency sound waves, a voice coil affixed to said dlaphragm, and means carried by said diaphragm having the double function of radiating high frequency sound waves and of supplying a cooling air current to said voice coil.

8. A relatively large conical diaphragm having means concentric with the axis thereof for setting up an unidirectional axial air current during vibratory movement of said diaphragm.

9. The invention set forth in claim 1, characterized in that the cooling means is constituted by a relatively small truncated conical diaphragm, the base of which is directed toward the voicecoil.

' HAROLD R. VOORHEES. 

